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<title>Algernon and Access-Limited Logic</title>
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<h1> Algernon and Access-Limited Logic </h1>

Access-limited logic, and its embodiment in a knowledge-representation
language named Algernon, has been a focus for research in the <!WA0><!WA0><!WA0><!WA0><!WA0><a
href="http://net.cs.utexas.edu/users/qr/"> Qualitative Reasoning group</a>.
  <p>

<ul>
 <li> <!WA1><!WA1><!WA1><!WA1><!WA1><a href="#Overview">Brief overview</a>.
 <li> <!WA2><!WA2><!WA2><!WA2><!WA2><a href="#Researchers"> Researchers</a>.
 <li> <!WA3><!WA3><!WA3><!WA3><!WA3><a href="#learning"> Learning About Algernon</a>.
 <li> <!WA4><!WA4><!WA4><!WA4><!WA4><a href="#references"> References</a>.
 <li> <!WA5><!WA5><!WA5><!WA5><!WA5><a href="#applications"> Applications</a>.
 <li> <!WA6><!WA6><!WA6><!WA6><!WA6><a href="#software"> Software</a>.
 <li> <!WA7><!WA7><!WA7><!WA7><!WA7><a href="#users"> Algernon users</a>.
</ul>

<h2> <a name="Overview">Brief Overview</a> </h2>

Access-Limited Logic is a language for representing knowledge in the
computer, and a method for drawing conclusions and answering questions
from that knowledge.  <p>

Previous languages and methods faced an apparently unsolvable conflict
between three important values: (1) having a clear and precise
meaning; (2) being computationally efficient; and (3) being able to
draw all correct conclusions eventually.  Part of the efficiency
problem is that, out of a vast amount of knowledge, it is hard to find
the right facts and rules to bring together.  <p>

Like humans, access-limited logic uses the connections between related
concepts to focus its search for useful information.  Although it is
possible to miss connections between concepts that lack an available
``access path,'' this method gives us values (1) and (2): clarity and
efficiency.  As for value (3), known as ``completeness'', for a
language expressive enough for common-sense knowledge, it is
impossible to draw all correct conclusions efficiently.  However, we
have shown that access-limited logic has the property of ``Socratic
completeness'': if a wise tutor asks the right series of questions,
any correct conclusion can be found (and each question will be
answered efficiently).  Furthermore, for most common-sense knowledge,
the series of questions to ask can usually be found efficiently.  <p>

In addition to our theoretical work on Access-Limited Logic, we have
implemented a system named Algernon that embodies its principles.
Algernon has been used for the graduate expert systems course at UT,
for research toward at least four doctoral dissertations, and as a
research tool at UT, MCC, and Stanford University.  MCC, in turn, has
distributed Algernon to its shareholders.  <p>

A more <!WA8><!WA8><!WA8><!WA8><!WA8><a href="http://www.cs.utexas.edu/users/qr/algernon-technical.html"> technical discussion of
Algernon and ALL</a> is also available.


<h2> <a name="Researchers"> Researchers </a> </h2>

<ul>
 <li> <!WA9><!WA9><!WA9><!WA9><!WA9><a href="http://www.cs.utexas.edu/users/kuipers"> Ben Kuipers</a> --- kuipers@cs.utexas.edu
 <li> <!WA10><!WA10><!WA10><!WA10><!WA10><a href="http://www.cs.utexas.edu/users/hewett"> Micheal Hewett</a> --- hewett@cs.utexas.edu
 <li> <!WA11><!WA11><!WA11><!WA11><!WA11><a href="http://cirl.uoregon.edu/crawford.html"> James Crawford</a> 
      --- jc@cs.uoregon.edu
</ul>



<h2> <a name="learning">Learning About Algernon</a> </h2>

 <ul>
  <li> B. J. Kuipers and J. M. Crawford.  1994.
<!WA12><!WA12><!WA12><!WA12><!WA12><a href="file://ftp.cs.utexas.edu/pub/qsim/algernon/algernon-reference-manual.ps.Z"> 
Short Algernon Reference Manual (for Algernon version 1.3.0)</a>.
Unpublished manuscript. <P>
 <ul>
  <li> As of this writing (4-18-94), the reference manual may be more recent
than the file algernon.tar.Z.
 </ul>
 <P>

 <li>  B. Kuipers.  1993.  
<!WA13><!WA13><!WA13><!WA13><!WA13><a href="file://ftp.cs.utexas.edu/pub/qsim/algernon/algernon-for-ES.ps.Z">
Algernon for Expert Systems</a>.  Unpublished manuscript. <P>
 <ul>
  <li>  This evolving document illustrates how to write code in Algernon for
various useful tasks.
 </ul>


 </ul>


<h2> <a name="references">References </a> </h2>

<ul>

  <li> Raman Rajagopalan.  1992.  
<!WA14><!WA14><!WA14><!WA14><!WA14><a href="file://ftp.cs.utexas.edu/pub/qsim/papers/Rajagopalan-aaai92-tract-reas-wkshp.ps.Z">
<b>Results of an experiment in domain knowledge base 
construction: a comparison of the Classic and Algernon knowledge 
representation systems.</b></a>  <CITE>Working Papers of the AAAI Workshop on Tractable
Reasoning</CITE>, AAAI-92, San Jose, CA, 1992.
  <p>

  <li> J. M. Crawford & B. J. Kuipers.  1991.  
<!WA15><!WA15><!WA15><!WA15><!WA15><a href="file://ftp.cs.utexas.edu/pub/qsim/papers/Crawford+Kuipers-SIGART-91.ps.Z">
<b>Algernon -- a tractable
system for knowledge representation.</b></a>  <i>SIGART Bulletin</i> 2(3): 35-44,
June 1991.
  <p>

  <li> J. M. Crawford & B. J. Kuipers.  1991.  
<!WA16><!WA16><!WA16><!WA16><!WA16><a href="file://ftp.cs.utexas.edu/pub/qsim/papers/Crawford+Kuipers-AAAI91.ps.Z">
<b>Negation and proof by
contradiction in access-limited logic.</b></a>  In <i>Proceedings of the National
Conference on Artificial Intelligence (AAAI-91)</i>, AAAI/MIT Press, 1991. 
  <p>

  <li> J. M. Crawford & B. J. Kuipers.  1991.  
<!WA17><!WA17><!WA17><!WA17><!WA17><a href="file://ftp.cs.utexas.edu/pub/qsim/papers/Crawford+Kuipers-sowa-91.ps.Z">
<b>ALL: formalizing access-limited reasoning.</b></a> In John Sowa (Ed.),
<i>Principles of Semantic Networks</i>, pp. 299-330.  San Mateo, CA:
Morgan Kaufmann.  <p>

  <li> James Crawford.  1990.
<!WA18><!WA18><!WA18><!WA18><!WA18><a href="file://ftp.cs.utexas.edu/pub/qsim/papers/Crawford-PhD-91.ps.Z">
<b>Access-Limited Logic: A Language for
Knowledge Representation</b></a>.  Doctoral dissertation, Department of
Computer Sciences, University of Texas at Austin, Austin, Texas.  UT
Artificial Intelligence TR AI90-141, October 1990.  
<!WA19><!WA19><!WA19><!WA19><!WA19><a href="file://ftp.cs.utexas.edu/pub/qsim/papers/Crawford-PhD-91-toc.ps.Z">
[Table of Contents]</a>.
 <p>

  <li> J. M. Crawford, A. Farquhar, B. J. Kuipers.  1990.  
<!WA20><!WA20><!WA20><!WA20><!WA20><a href="file://ftp.cs.utexas.edu/pub/qsim/papers/Crawford+Farquhar+Kuipers-AAAI90.ps.Z">
<b>QPC: a
compiler from physical models into qualitative differential equations.</b></a>
<i>Proceedings of the National Conference on Artificial Intelligence
(AAAI-90)</i>, AAAI/MIT Press, 1990. 
  <p>

 Revised version in Boi Faltings and
Peter Struss (Eds.), <i>Recent Advances in Qualitative Physics</i>, MIT
Press, 1992. <p>

  <li> J. M. Crawford and B. J. Kuipers.  1989.  
<!WA21><!WA21><!WA21><!WA21><!WA21><a href="file://ftp.cs.utexas.edu/pub/qsim/papers/Crawford+Kuipers-kr-89.ps.Z">
<b>Toward a theory of access-limited logic for knowledge representation.</b></a>
In <i>Proceedings of the First International Conference on Principles
of Knowledge Representation and Reasoning (KR'89)</i>.  Los Altos,
CA: Morgan Kaufmann.  <p>

</ul>


<h2> <a name="applications">Applications </a> </h2>

Several doctoral dissertations have used Algernon as a central part of the 
implementation.

<ul>

  <li> Adam Farquhar.  1993.  
<!WA22><!WA22><!WA22><!WA22><!WA22><a href="file://ftp.cs.utexas.edu/pub/qsim/papers/Farquhar-PhD-93.ps.Z">
<b>Automated modeling of physical systems
in the presence of incomplete knowledge.</b></a>   University of Texas at
Austin, Artificial Intelligence Laboratory, Technical Report AI
93-207.  (Doctoral dissertation, Department of Computer Sciences.)
  <p>

  <li> Jeff W. Rickel.  1995.  
<!WA23><!WA23><!WA23><!WA23><!WA23><a href="file://ftp.cs.utexas.edu/pub/qsim/papers/Rickel-PhD-95.ps.Z">
<B>Automated modeling of complex
systems to answer prediction questions.</B></a>  Doctoral dissertation,
Department of Computer Sciences, The University of Texas at Austin.
(Available as technical report AI95-234.)
 <P>

  <li> Raman Rajagopalan.  1995.  
<!WA24><!WA24><!WA24><!WA24><!WA24><a href="file://ftp.cs.utexas.edu/pub/qsim/papers/Rajagopalan-PhD-95.ps.Z">
<B>Qualitative reasoning about
dynamic change in the spatial properties of a physical system.</B></a>
Doctoral dissertation, Department of Computer Sciences, The University
of Texas at Austin.  (Available as TR AI95-241.)
 <P>


</ul>


<h2> <a name="software"> Software </a> </h2>

The source codes for <!WA25><!WA25><!WA25><!WA25><!WA25><a href="http://www.cs.utexas.edu/users/qr/QR-software.html"> Algernon and QPC are
available</a>.
 <ul>
  <li> AT+T Bell Labs has created R++, a rule-based extension to C++,
       based on the ideas of access-limited logic developed in Algernon.
       <!WA26><!WA26><!WA26><!WA26><!WA26><a href="http://www.research.att.com/sw/tools/r++/">
       R++ is available</a> to university researchers.
 </ul>


<h2> <a name="users"> Algernon Users and History </a> </h2>

Ben Kuipers initially conceived of Algernon and Access-Limited Logic
as a synthesis of frames and logic-based approaches to knowledge
representation while teaching an undergraduate class on AI programming
methods.  He has used Algernon as the programming vehicle for his
Expert Systems class at the University of Texas for a number of years.
<p>

James Crawford did all of the theory of Access-Limited Logic,
including inventing the key concept of "Socratic Completeness", and
did a near-complete reimplementation of Algernon.  Crawford's PhD
thesis is the definitive description of Access-Limited Logic.  <p>

QPC, our compositional compiler for qualitative models, is implemented
in Algernon.  This was initially a collaboration between Adam
Farquhar, James Crawford, and Ben Kuipers, and grew into Adam
Farquhar's PhD thesis.  <p>

Raman Rajagopalan and Jeff Rickel did their PhD research using QPC,
and were thus regular Algernon users. <p>

Chinatsu Aone did a PhD thesis in linguistics on the understanding of
quantified expressions, and used Algernon as the knowledge
representation language.  She convinced MCC to provide Algernon as one
of the knowledge representation languages for their NLKB (Natural
Language Knowledge Base) project.  <p>

Elias Costopoulos implemented Algernon in C++ for the PC.  <p>

Omid Sojoodi-Haghighi implemented the KM system based on the ideas in 
Access-Limited Logic, though not on Algernon.  KM is currently the
representation language for the Biology KB group.  <p>

Mike Hewett is investigating ways to make the Algernon implementation
more robust and efficient.  <p>


<hr>
<!WA27><!WA27><!WA27><!WA27><!WA27><a href="http://www.cs.utexas.edu/users/qr">[QR home]</a>

<address><!WA28><!WA28><!WA28><!WA28><!WA28><a href="http://www.cs.utexas.edu/users/kuipers">BJK</a></address>
